Estrogen and progesterone: you've been hearing about them since you were a kid in middle-school health class. Starting during puberty, they affect your body in critical ways – and if you have breast cancer, they can mean the difference between life and death.
What are hormones?
Think of hormones as part of your body's communication system. Hormones are chemicals; they're manufactured in one part of your body, then travel to another part to direct and control certain processes.
Estrogen, the chief female sex hormone, is manufactured in the ovaries (as well as by the adrenal glands and in fat tissue, to a lesser degree). It then travels throughout the body, regulating a number of diverse areas, from your menstrual cycle to body weight to bone density.
How estrogen's role changes over time.
During puberty, estrogen tells your breasts it's time to grow. It also instigates the development of secondary sexual characteristics (e.g., pubic hair, widened hips). If you become pregnant, estrogen works with progesterone to insure you won't continue to ovulate during pregnancy.
As you age, estrogen helps keep your skin and hair young-looking and healthy, and maintains your sex drive. It also works to keep your bones strong by preventing the natural bone rebuilding process from slowing down due to age.
When you go through menopause, your body slows its estrogen production way down. Which is why menopause comes with so many difficult side effects, from vaginal dryness and loss of libido, to weight gain, and aging skin and hair. To say nothing of hot flashes, which result from age-based fluctuations in your usual steady supply of estrogen.
Estrogen can cause breast pain.
During your monthly cycle, estrogen causes your breasts to prepare for possible pregnancy by growing new cells and amping up blood supply. This is why your breasts may feel sore and full just before your period.
If you don't become pregnant, these new cells gradually die and are absorbed. But sometimes, over the course of years, scar tissue can develop from this continuing growth/death process; and this scar tissue becomes a fibroadenoma, a lump you can feel. Often, these lumps press on nerves and are painful.
Higher estrogen levels raise breast cancer risk.
Hormone replacement therapy (HRT), medication that raises estrogen levels, is taken by some women to relieve menopausal symptoms. Solid evidence exists that taking HRT at more than a minimal dose, for longer than two or three years, raises breast cancer risk in healthy women.
Since estrogen is manufactured by body fat, overweight women have higher estrogen levels than women of normal weight, and are also at increased risk of breast cancer.
Estrogen can cause a breast cancer recurrence.
If you've been diagnosed with breast cancer, you may have heard your doctor say that your cancer is hormone-responsive, or estrogen/progesterone positive (ER/PR+). About 85 percent of all breast cancers are hormone-responsive – which means the cancer cells rely on estrogen, and possibly progesterone, to stay alive and reproduce. (While doctors commonly link estrogen and progesterone when talking about their effect on recurrence risk, estrogen's effect is much more certain; researchers are still on the fence about progesterone.)
Estrogen's strong positive influence on breast cancer cells is the reason you might be prescribed hormone therapy: a 5- to 10-year course of drugs designed to lessen cancer cells' access to estrogen. Tamoxifen, commonly taken by pre-menopausal women, "plugs up" cancer cells' receptors, making them unable to absorb estrogen. Aromatase inhibitors (Femara, Aromasin, Arimidex), usually taken by women who've been through menopause, actually lower the body's production of estrogen to minimal levels, lower even than what's common for older women. Either way, cancer cells can't get the estrogen they need, and they die.
What can you do to control estrogen levels?
If you feel your estrogen level is too low – you're experiencing debilitating hot flashes, mood swings, and other disruptive menopausal symptoms – speak with your doctor about a short course of low-level HRT.
If you're at high risk of breast cancer – either due to family history, BRCA genetic mutations, or a previous personal history of breast cancer – your doctor will probably want you to take hormone therapy: drugs that lower your estrogen level (or prevent it from doing its work). Taking these drugs regularly, for as long as your doctor recommends, is the best way science knows (at the moment) to lower your risk of hormone-receptive breast cancer.
See more helpful articles:
A Guide to Breast Cancer Treatment
Hormone Therapy vs. Hormone Replacement Therapy: What's the Difference?
Top 10 Breast Cancer Risk Factors
Mayo Clinic Staff. "Breast Cancer Chemoprevention: Medicines That Reduce Breast Cancer Risk." Mayo Clinic. February 12, 2014.
"Normal Testosterone and Estrogen Levels in Women." WebMD. Accessed June 28, 2015.
Breast cancer survivor and award-winning author PJ Hamel, a long-time contributor to the HealthCentral community, counsels women with breast cancer through the volunteer program at her local hospital. She founded and manages a large and active online survivor support network.